Fog penetrating light



June 29, 1965 M. P. DEPUTY 3,192,438

FOG PENETRATING LIGHT Filed Aug. 15, 1962 v /A/VNTOR MARSHALL R DEPUTY United States Patent 3,192,438 FOG PENETRATING LIGHT Marshall P. Deputy, La Grange, lll., assignor to Fog- Master Corporation, La Grange, Ill., a corporation of Illinois Filed Aug. 13, 1962, Ser. No. 216,551

4 Claims. (Cl. 315-209) This invention relates to a fog penetrating light and method of penetrating fog and more particularly to the production of a light beam for signalling or for illuminating objects through fogs.

When a light beam is directed into a fog it strikes the particles of water suspended in the air and is diffused by them in a relatively short distance. When the beam is used for illumination these lighted particles appear as a milky curtain between the observer and the objects to be illuminated and effectively cut off all vision beyond a very short distance. This condition can create dangerous situations for vehicular trafiic whether highway, boat or aircraft, and prevent adequate illumination or fog penetration for other purposes. A satisfactory answer to the problem of fog penetration by light beams is the visible portion of the spectrum has long been sought.

Increasing the intensity of the light beam has been attempted, but is not a satisfactory answer. In the first place, there are practical limitations to the intensity of lights which can be used, particularly in highway trafiic. Perhaps more important is the fact that any increases in fog penetration resulting from increased intensity of the beam are offset by increased intensity of the milky curtain so that the gain in actual visibility is negligible and may even be a loss.

Use of lamps with filters of different colors has been attempted, but has not provided a satisfactory answer. While the longer wave lengths toward the red end of the spectrum may not diffuse as much as white light, their visibility is also less than that of white light. The gain in visibility from the use of filters or lenses of different colors is, therefore, negligible.

It is an object of the present invention to provide a fog light and method of penetrating fog by which penetration of fog by visible light is very substantially increased over lights as heretofore known.

- Another object is to provide a fog light and method of penetrating-fog in which the light beam is periodically reduced in intensity or extinguished in relatively rapid cycles.

The present invention is based on the observed phenomenon that when a light such as an automobile headlight is first turned on, objects at a substantial distance are momentarily visible but are quickly hidden by the milky curtain generated by the fog. While not established to the point of certainty, it is believed that this phenomenon occurs because diffusion of the light to illuminate the water particles in the atmosphere is cumulative and that the initial light beam during the first fraction of a second penetrates to a greater extent between the water particles with less illumination of the water particles themselves than occurs after the light has been on for a longer interval.

It follows, therefore, that if the light is turned on and off in fairly rapid cycles diffusion will not accumulate to the point of creating a milky appearance in the atmos phere and that objects will be visible for a much greater distance than would be the case with a steady light.

It has been found that there are certain critical relationships as to time on to time off during a cycle and length of cycle to intensity which must be observed for optimum results. For example, the light must be energized during about three-fourths of each cycle and de-energized during ICC about one-fourth of each cycle. If the light is energized for a lesser percentage of the cycle, the total effective illumination is reduced while if it is energized for a greater percentage diffusion will increase and the period during which it is tie-energized will be too short to allow the light to go out or to reduce its intensity to a sufficient degree.

The light used, whether of the filament or gaseous discharge type, Will not be extinguished instantaneously when it is de-energized but will continue to emit light for a short interval. The filament of a filament lamp requires some time to cool and the ion glow of a gaseous discharge lamp persists after the energizing voltage its removed. I have found that for the purposes of the present invention the light must be de-energized long enough to permit its emission rate to drop to one-half or less of its normally energized emission rate.

The factor also limits the cycle length or frequency of cycling since the cycle must be long enough to allow the light emission from the lamp to fall to less than one-half its normal value during the portion of the cycle when it is de-energize-d. Since the larger more powerful lamps continue to emit light for a longer time after being deenergized, this means that the cycle length must increase as the power of the lamps increases.

Specifically, it has been found that a lamp of from about 28,000 to about 36,000 candlepower should be cycled about 101 times per minute giving a cycle length of about .6 second. The emissivity of a 36,000 candlepower lamp will drop to about 16,000 candlepower during the time it is de-energized, which occupies about .15 second of each cycle. A 50,000 candlepower lamp should be cycled about times per minute giving a cycle length of about .67 second. A lamp of 800,000 candlepower should be cycled about 27 times per minute giving a cycle length of about 2.2 seconds. Cycles longer than about 2.2 seconds are not practical regardless of the intensity of the light.

It has been found that with lamps of 50,000 candlepower or more, there may be a glow zone, or a zone in which the water particles are more or less illuminated, immediately in front of the lamp. With a 50,000 candlepower lamp no glow zone is observable in a number three fog but in a number seven fog the glow zone extends outward about forty feet. With an 800,000 candlepower lamp the glow zone extends about thirty feet in a number three fog, about sixty feet in a number five fog and about seventy-five feet in a number seven fog. Even though objects are not visible through the more intense glow zones, it has been found that the light penetrates and illuminates objects beyond the glow zones so that the objects are readily visible from positions at one side of the lamp. If the rate of cycling is increased the glow zone is extended furtherout and the penetration decreases. This is believed to be due to the fact that the light intensity does not drop far enough when the light is tie-energized so that it approaches the condition of a steady light. On the other hand, it has been found that if the rate of cycling is decreased the penetration also decreases. This is believed to be due to the fact that the average intensity of illumination is decreased.

While a single lamp may be used satisfactorily for signailing, it is not satisfactory for either illuminating purposes or for running lights on a vehicle because the flickering effect due to cycling of the light quickly produces eye fatigue. A light having a more uniform appearance is also preferred for many types of signal lights such as aircraft beacon lights, runway lights, and the like.

For these purposes, it is preferred to employ a plurality of lights, preferably at least three, which are so arranged that their beams are overlapping and which are of different intensity. The difference in intensity may be achieved by using lamps of different power or by using Patented June 29, 1965 6 identical lamps with different lenses as, for example, lenses of different colors which will filter out more or less of the light and give an eifect of different intensity light sources. I have found that for effective operation the several lights must differ in intensity one from the other by from to 10 percent. If the difference between the intensity of the lamps is greater than this amount, the penetrating effect and illumination is less while if the difference between the successive lamps is less than about 5 percent, the light will diffuse to produce the milky curtain-etfect mentioned above. The lamps are operated in overlapping cycles as described above and with each lamp being energized for about three-fourths of each cycle, it will be seen that at least two of the lamps are energized at all times and that during very brief intervals all three of the lamps are simultaneously energized.

In. one unit constructed according to the invention, three lamps were employed each having a nominal intensity of-36,000 candlepower and each operated at a flashing frequency of 101 cycles per minute with the cycles equally spaced each from the next. One of the lamps employed a lens producing an 11 percent loss, the second lamp a lens producing a 17 percent loss and the third a lens producing a 22 percent loss. with this unit that objects were readily visible through a number seven fog at a distance of at least 175 feet.

In another unit, three lamps were employed each having a nominal intensity of 22,000 candlepower each and using filter lenses reducing the intensities of the lamps by the same percentages as in the first example. Itwas found that with this unit road signs were visible through a number five fog at 127 feet.

. In tests of still another unit using three lamps of 277,000 nominal candlepower' each and with filtering lenses comparable to those in the first example, it was found that blotters having light absorptive surfaces were visible at 422 feet in a number five fog and that a painted truck body was visible at 725 feet in the same fog.

In tests of larger unit using three lamps of 800,000 candlepower each with filtering lenses comparable to those used in the first example, objects were visible at 790 feet through a number six fog. In this case the objects could not be seen throughthe glow zone by an observer close to the lamp but could be seen by observers at the sides of the. lamp far enough from it to be out of line with the glow zone.

The accompanying drawings illustrate diagrammatically different arrangements for carrying out the invention and on automobiles and similar vehicles, including a glass en-.

velope 10 within which a filament 11 is mounted. It will be understood that'the interior of the glass envelope is silveredor otherwise formed with a reflecting surface over all except the front area 12, which may be formed as a lens to ditfuse or direct the light in any desired manner. l

The filament may be energized from any suitable source of power shown as a battery 13 which is connected to the filament through a switch 14. The switch is actuated by a rotary cam 15 having a single raised lobe 16 extending through approximately one-fourth of its circumference with the remainder of its circumference being circular. The cam may be driven by a motor 17 'of the synchronous type which will turn the cam at a substantially'uniform speed. I

With the battery connected to the lamp and the motor 17 running, the switch 14 will be closed to energize the filament 11 except when the lobe 16 of the cam engages an actuating'projection on the switch blade to open it.

It was found in tests assaass In this way, the switch will be open throughout approximately one-fourth of a complete cycle of the cam and will be closed to energize the filament during the remaining three-fourths of the cycle. The motor may be operated to drive the cam at a speed such as to produce the desired cycle length depending uponthe candlepower of the lamp, as described above.

FIG. 2' illustrates an arrangement of three lamps 20, 21, and 22,.accordin'g to the invention which'are either of different candlepower or which are,'as described above, provided with lenses of different colors to create more or less of a light loss in transmission. For example, the lamp 250 may be providedwith a white lens which will create the minimum amount of loss, the lamp 21 with a light amber lens which will create a greater loss, and the lamp 2?. with a dark amber lens which will produce a still greater loss. The lamps are connected in parallel to a source of power shown as a battery 23 and are controlled by switches 24, 25 and 26, respectively, which are operated by a rotary cam 27, similar to the cam 15 of FIG. 1. The cam 27 is'provided with a single raised lobe 28' extending through approximately one-fourth of its circumference and which successively engages and opens the switches as the cam rotates. f

It will be seen that with this construction the lamps are successively energized and de-energized in cycles in which each lamp remains energized through approximately three-fourths of the cycle and de-energized through approximately the remaining one-fourth of the cycle. The cycles are successive and overlapping so that at least two of the lamps are energized at all times and for brief intervals all three of the lamps are energized. Itwill be understood that the speedof the cam is controlled to provide cycles of appropriate length for the intensity of the lamps, as described'above.

By the use of three separate lamps asshown in FIG. 2 operated in overlapping cycles and of different intensities it has been found that the illumination gives the appearance of being more nearly constant than with a single lamp, even though there are frequent changes in intensity of the light. Thus with a construction of this type eye fatigue is minimized while penetration of fog by the light is equally as good as that obtained with a single lamp or perhaps even better.

While the invention has been described in connection with two particular arrangements embodying one and three lamps, respectively, it will be understood that these are not intended to limit the scope ofthe invention, but are for purposes of illustration only. Reference will therefore be had to the appended claims to determine the scope of the invention.

What is claimed is: i

1.;The method of penetrating fog with a light beam whichcornprises directing a light beam through a foggy atmosphere and reducing the intensity of the beam to less than one-half its normal intensity during approximately one-fourth of each of a series of cycles varying in length from about .6 second to about 2.2 seconds.

2. The method of claim 1 in which the lengthof the cyclesisincreased as the intensity of the light beam increases.

3. The method of penetrating fog with light which comprises directing at least three overlapping light beams through a foggy atmosphere,'said light beams varying in normal intensity by from 5 percent to 10 percent from one beam to the next, and periodically reducing the normal intensity of the beams by at least one-half in'overlapping cycles of a length from about .6 second-to about 2.2 seconds with each beam being at, normal intensity for about three-fourths of each cycle so that atleast two of the beams are of normal intensity at all times.

'4; Afog penetrating light comprising. at least three electric lamps, each of lamps producing light of different intensity diifering by about 5 percent to about 10 percent from one lamp to thenext and the lamps being adjusted- 5 6 to produce overlapping beams, connections from the lamps. References Cited by the Examiner to a source of current, switches in the connections 0011- UNITED STATES PATENTS trolling the lamps respectively, and means for operating the switches in successive overlapping cycles of from about 214811225 9/49 Kaye 31582 X .6 second to about 2.2 seconds with each lamp being ener- 5 DA ID I AL IN P gized during about three-fourths of each cycle so that at V G V Exammer' least two of the lamps are energized at all times. JAMES KALLAM, Examiner- 

1. THE METHOD OF PENETRATING FOG WITH A LIGHT BEAM WHICH COMPRISES DIRECTING A LIGHT BEAM THROUGH A FOGGY ATMOSPHERE AND REDUCING THE INTENSITY OF THE BEAM TO LESS THAN ONE-HALF ITS NORMAL INTENSITY DURING APPROXIMATELY ONE-FOURTH OF EACH OF A SERIES OF CYCLES VARYING IN LENGTH FROM ABOUT .6 SECOND TO ABOUT 2.2 SECONDS. 